There are many published examples of structures designed to achieve the above mentioned effect. One such example consists of a first, metal casing surrounding the stage of aerofoils, the metal casing itself being surrounded by an annular metal honeycomb structure, followed by a further metal casing surrounding the honeycomb structure, and followed again by multiple wrappings of a fibrous material such as Kevlar around the further metal casing.
A further example comprises a ring fitted in the first metal casing surrounding the stage of aerofoils, which ring, on being struck by a broken off aerofoil, is caused to rotate, thus absorbing the kinetic energy expended by the broken off aerofoil, to an extent that prevents the aerofoil puncturing the casing wall and exiting the engine.
All the known published art consists of assemblies of one piece members, each member being truly circular in form. The present invention seeks to provide an improved aerofoil containment structure.